Method of producing vitreous layers on substrate materials

ABSTRACT

A method of producing vitreous layers on any type of substrate material in which an alkali-containing multi-component glass having at the most 10 percent by weight of alkali oxide is heated in an electron beam furnace to a glowing condition and then is subjected to the action of the electron beam which vaporizes the pre-heated glass and deposits it on the substrate material.

United States Patent Mulfinger et al. Apr. 2, 1974 [54] METHOD OFPRODUCING VITREOUS 3,421,916 1/1969 Mikoda 65/33 LAYERS 0N SUBSTRATEMATERIALS 35371868 11/1970 KPSaka 1 3,647,490 3/1972 Plrooz 65/33 [76]In HanS-0tt0 Mulfinger, 3,645,786 2 1972 Tannenberger 117 106Alemannenstrasse 24, Ingelheim/Rhine; Hubert Dutz, OTHER PUBLICATIONSxgfig g gfi gfi f Moore, David; Electron Beam Technology, Evapora- 1 S gtion b Electron Bombardment, 1962, p. 387-388. Krolla, Westrmg 285, yMainz-Mombach, all of Germany Primary ExaminerRalph S. Kendall [22]Filed Sept 1971 Assistant Examiner-J. Massie [21] App]. No.; 181,020Attorney, Agent, or Firml-lill, Sherman, Meroni,

G o & Sim son Related US. Application Data r SS p [63]Continuation-in-part of Ser. No. 791,427, Jan. 15,

1969, abandoned. [57] ABSTRACT 52 us. (:1. 117/935 117/106 A 117/169 A APmducing "mews layers any type 65/33 substrate material in which analkali-containing multi- [51] Int CL C23: 13/04 component glass havingat the most 10 percent by [58] Field g g 70 93 3 weight of alkali oxideis heated in an electron beam furnace to a glowing condition and then issubjected to the action of the electron beam which vaporizes the [56]References Cited pre-heated glass and deposits it on the substratematerial.

3 Claims, 1 Drawing Figure METHOD OF PRODUCING VITREOUS LAYERS ONSUBSTRATE MATERIALS The invention relates to a method of producingvitreous layers on any kind of substrate materials by means of electronbeam furnaces'in a high vacuum, and constitutes a continuation-in-partof application Ser. No. 791,427 filed on Jan. 15, 1969, now abandoned.

There are known several methods for vapordepositing vitreous layers onsubstrates.

One of these prior methods consists in this, that highly oxidizablemetals or metal alloys, as for instance lead-silicon, lead-tellurium,aluminum-silicon, in the form of an electrode are vaporized in anoxygen-argon gas atmosphere at a total pressure of approximately 2.5 X10' torr and are precipitated as oxide on the substrate. This method islimited to metals as starting material and also to the vaporization ofsolids as vapor depositing process. This known method requires further arelatively high partial pressure of oxygen of about 1.2 X 10 torr andfor this reason alone is not suitable for vapor depositing by means ofelectron beams which takes place at pressures of less than 10 torr.Nothing is stated about the quality of the films to be vapordeposited.This method is limited to obtainable alloys; and it will not permit theintroduction of network moditiers, such as lithium, sodium, potassium,etc., into the glass layer to be produced.

Another method is based on a plurality of metal oxides which areseparately heated in a vessel and are vaporized at 10 torr. Thedisadvantage of this known method is that it is very difficult to obtainhomogenous glasses from separately vaporized oxides.

It is further known to vapor deposit vitreous monocomponent layers bymeans of electron beam furnaces in a high vacuum. Such layers whichconsist of quartz are, however, composed of a plurality of individualparticles and are, therefore, not dense but cracked or fissured, so thattheir possibilities for use are limited.

The object of the invention is a method of producing vitreous coatingson any type of substrate materials by means of electron beam furnaces ina high vacuum, by which the coatings obtained are homogeneous, have notendency to form fissures and are free from the further disadvantages ofknown methods.

This object is attained according to the invention in that analkali-containing multi-component glass including at the most percent byweight of an alkali oxide is to a high degree degassed in vacuo or ismelted in a protective gas atmosphere, and is subsequently vaporized andprecipitated on the substrate.

Depending upon the manufacturing conditions and the intended use, theselayers or coatings may possess one or more of the following properties:They may be dense, hard, flexible, they may be either electricallynon-conductive or semi-conductive, anti-static, hydrolytically stable,transparent, they may have a high or a low index of refraction, they maybe colorless as well as colored, heat-insulating and they may have verygreat electric strength. For special purposes, a number of differentmulti-component glasses may be vapordeposited superimposed in severallayers.

The method of the invention thus opens up a multitude of new fields ofapplication.

Care should be taken that the water content be kept as low as possibleby insertion of dry raw materials.

Furthermore, glass compositions inclined to give off larger amounts ofoxygen are not well suited.

As a protective gas for the melting process may, for instance, be useddried air, nitrogen or rare gases.

As unfavorable have proven glasses which have a high percentage ofconstituents whose vapor pressure is much greater than the pressure inthe recipient during treatment in vacuum. Therefore, according to theinvention, the multi-component glasses are indeed to contain alkali, butnot more than 10 percent by weight of alkali oxide.

As particularly advantageous has proven to be alkali borosilicate glasswhose boric acid content is not more than 25 percent by weight.

According to the invention, also partly crystallized, or dissociatedmulti-component glasses may be vaporized and precipitated. In this way,it is made possible to utilize glasses for the method which in othercases leads to disadvantageous crystallization or dissociation during aheat treatment.

It has been discovered that the method of the invention is particularlysuitable for multi-component glasses which contain the followingcomponents either singly or combined: Oxide of the first, second, third,fourth and fifth main group and oxides of the first, second, third,fourth, fifth, sixth, seventh and eighth sub-groups of the periodicsystem of the elements, particularly, however, those of lithium, sodium,potassium, barium, titanium, vanadium, niobium, tantalum, boron,aluminum, gallium, silicon, germanium and phosphorus.

According to another feature of the invention, a high melting butreadily vaporizable alkaliborosilicate glass may be dissolved in alow-melting glass which, however, is difficult to vaporize, or it may beintimately mixed with it, and this solution or mixture, respectively,serves as a multi-component glass to be vaporized. In this manner, thenumber of suitable multi-component glasses coming into considerationwith their special properties is considerably increased.

The multi-component glasses used in accordance with the method of theinvention preferably have the following composition.

SlOz- 35 percent by weight 8 0 -5 25 percent by weight Li O-0 5 percentby weight Na O0.5 10 percent by weight K O0.5 10 percent by weight Al O3 40 percent by weight CaO-0-25 percent by weight BaO-025 percent byweight TiO2-0-20 percent by weight V O50 50 percent by weight Infidertoobtainthic k ia ers'arrayer packs, the invention proposes tovapor-deposit one or more multicomponent glasses simultaneously oralternately on a selected substrate material.

Since by the use of electron beam furnaces the multicomponent glass israpidly heated to high temperatures and undergoes a heat shock, thethermal coefficeint of expansion should preferably be 40 X l0"/C in therange from 20 to 300C.

In order to be able to use also multi-component glasses for the methodof the invention, such multicomponent glasses are heated by a heatingdevice prior to commencement of vaporization to a temperature above thelower limit of the cooling temperature.

While the prior known vapor-deposited layers, particularly those havinga crystalline structure, disclose more or less strong tensile stresseswhich may lead to the formation of fissures or cause a chipping off from.the substrate already at layer thickness above 0.1 pm,

the vitreous layers produced according to the inventionare largely freefrom tensile stresses and, owing to their excellent adherence toconventional substrate material are stable, even at relatively greatthicknesses. These properties also make it possible to impart a furtherfirmness-increasing effect to the layers in that with a suitableselection of materials, the condensation of the vaporized glass iscarried out in such manner that permanent compressive stresses areproduced in the coating. This is particularly successful on bases havinga good adhesive power, for instance glass surfaces, if a multi-componentglass whose coefficient of thermal expansion before and/or aftervaporization and condensation on the substrate is lower than that of thesubstrate material, is vaporized and precipitated on the substrate whileits temperature is maintained higher than the normal workingtemperature. After cooling to normal temperature, tangential compressivestresses are produced in the condensated layer which effect an increasein the mechanical strength and the surface hardness of the substrate.The layer thickness for this purpose should be at least several pm. Forthe heretofore unsolved problem of obtaining an effectivesurface-hardening of glass or ceramic materials by means ofvapor-deposited coatings without employing diffusion processes, themethod according to the new method opens up new possibilities for asimple technical solution.

The compact structure of the layers obtained in accordance with themethod of the invention, which layers have a volume factor very close to1, imparts to them at the same time a high degree of protection againstatmospheric and chemical influences which in most cases are alreadyobtained at small layer thicknesses. In this manner, optical glasses orcrystals for instance may be provided with optically satisfactoryprotective coatings. Also metal and plastic surfaces may be glazedaccording to the invention. The layers are further adapted to form aprotective covering and shielding of mechanically sensitive surfaces, asfor instance thin-film-switches or surface mirrors, and for sealing andinsulating non-homogeneous surfaces, such as fiber-optical plates.

EXAMPLE 1 C A mixture of 8,080 g SiO 2,240 g boric acid, 232 g A1 628 gsodium carbonate, 150 g sodium chloride, 91 g potassium carbonate wasmelted in portions in a platinum crucible at temperatures between l,550and 1,600C. The platinum crucible is placed in an evacuable andinductively heated furnace. The molten glass for clarification is heatedto 1,620C. Then a careful evacuation takes place until a pressure ofless than torr has been reached. This requires about twelve hours. Thenthe molten glass is poured into a mold and cooled in customary manneruntil it has become solid. Preferably the period of time required forevacuation is shortened by agitating the glass. The glass produced inthis manne r has thejollowing composition:

SiOZ 82.3 percent b y weight B O 11.7 percent by weight A1 O -2.9percent by weight Na2O2.71 percent by weight 4 KEG-0.4 percent by weightIt has the following characteristics: a 29.0 10" l/ C Tg 555 C 5 VA1,412 C Density 2.20 g/cm Tk b.100 254 C hydrolytic Class 1 A pane ordisc made of this glass is inserted in an electron beam furnace ofconventional construction in such manner that it may be rotated duringthe vaporizing operation. The electron beam is deflected 180, onto thesurface of the pane of glass so that the glass may be vapor-depositedunhindered on the substrate. Before the electron beam is turned on, thepane of glass is heated to a glowing condition. When using this particular glass, the electron beam may immediately be fully turned onbecause the thermic stresses will not destroy the glass. The glass maybe vapor-deposited on any type of substrate materials of desired shape.However, bodies with three-dimensional expansion must be rotated in twoplanes.

The vapor-deposited layer has the following characteristics: It isdense, transparent, flexible within a short radium, antistatic,fissure-proof, electrically insulating, thermically insulating,hydrolytically of very good stability.

EXAMPLE 2 A glass with the following composition: SiOz 80.90 percent byweight B20 12.8 percent by weight A1 0 2.2 percent by weight Na2O 5percent by weight K 0 0.6 percent by weight is ground in a porcelainmill with balls of procelain for as long atimeilntil 91 percent 10 g and46 percent 5 ;1.. 1,000 g of this powder are placed in a platinumcrucible which is placed in an inductively heated vacuum furnace. Theglass powder is heated for removal of the surface water to 580 C, and atthe same time the pressure is decreased to 0.1 torr. At this temperaturethe glass is left for 4 hours. Thereafter, the temperature is increasedto 700720 C. Simultaneously the pres sure is lowered to 0.05 torr. Thistemperature is maintained for 20 hours. The result is that the waterbound in the glass escapes. Subsequently the glass is heated in a shorttime to 1,l00 C. This temperature is maintained for 2 hours. Now theglass is heated to l,500 and left for 1 hour at this temperature.Thereafter the molten glass is poured into a mold and cooled as usualuntil it has become solid.

The glass produced in this manner has the following composition:

SiO -81.9 percent by weight B2O 13.0 percent by weight Al O 5.1 percentby weight Na O2.0 percent by weight K2O-0.5 percent by weight Furthercharacteristics:

The characteristics of this glass are to a far-going extent identicalwith those mentioned in respect of Example 1. Also the composition andthe characteristics of the vapor-deposited layer show hardly anydifferences from that in respect of Example 1.

EXAMPLE 3 A batch of the composition SiO2-3,O50 g B2O (dehydrated)-400 gA1 O 200 g Li CO 100 g Na CO 172 g CaCO 71 g BaCO 181 g LiF- 70g isplaced in a platinum crucible in an electrically heated furnace at attemperature of l,500. After the melting of the batch, the temperature isincreased within 2 hours to 1,650". For clarification the molten glassis left at this temperature for 10 hours. Thereafter, the temperature islowered to l,500 in /2 hour and then the molten glass is poured into amold and cooled as usual until it has become solid. During theintroduction-and melting-process, the furnace is flushed with highlydried air.

On account of the low content of alkali oxide and the low water contentobtained by this method, the glass shows excellent vaporizationcharacteristics.

EXAMPLE 4 A batch of the composition SiO 4,610 g B (anhydrous) 1,500 gBaCO 1,600 g CaCO 3,160 g Na CO 516 g LiF 176 g is placed in a platinumcrucible and heated in an electrically heated furnace of the ordinaryconstruction at l,450 C and melted, while the furnace is flushed withhighly dried air. The temperature is then increased to l,500 and in themeantime the molten glass is agitated to hasten the clarification. Thetemperature is left for 3 hours at l,500 while the flushing iscontinued. Thereafter the temperature is lowered during agitation to1,400 and the molten glass is poured into a mold and cooled as usualuntil solidification.

The vaporization characteristics of this glass are very good on accountof the low content of alkali oxide and the low water content of thesmelting method utilized.

EXAMPLE 5 A batch of the following composition:

SiO 7,330 g B 0 (anhydrous) 1,810 g Na O 143 g is melted in aplatinum-iridium-crucible in an electrically heated furnace at l,550 C.while the furnace is flushed with highly dried air. After the melting,the temperature is increased in 2 hours to l,700 C. For theclarification, the temperature is left for 8 hours. After this, thetemperature is lowered during continuous flushing with dry air to 1,600and the molten glass is poured into a mold and cooled as usual until ithas become solid. By means of a tempering treatment at 1,200, the glassis converted to a partially crystalline condition. This glass, uponvaporizing in an electron beam furnace, as described in Example 1, showsexcellent characteristics.

5 EXAMPLE 6 A batch of the composition: SiO 7,015 g B 0 (anhydrous)1,770 g A1 0 400 g Ba CO 1,300 g Ca CO 360 g Na CO 520 g LiF 175 g ismelted at 1,400 in a platinum crucible in an electrically heatedfurnace, while in the meantime the furnace is flushed with highly driedair. After the melting, the glass is heated, while being agitated, to1,600 and for the clarification is left for 3 hours at this temperature.During continuous flushing with dry air, the molten glass is cooledduring agitation to 1,400", then is poured into a mold and cooled asusual until it has become solid. On account of the dissociationoccurring, this glass is white-opaque.

The vaporization characteristics of this glass are very good.

The method according to the invention will now be explained in greaterdetail in an embodiment by way of example, with reference to the singleFIGURE of the accompanying drawing, in which a device for performing themethod is diagrammatically illustrated.

Within a casing formed by a shell 10 which is evacuated and sealedagainst the outer atmosphere is arranged a vertically disposed shaft 1,a motor 3, which drives a horizontal shaft 4 which in turn rotates by abevel gear transmission the vertical shaft 1. The upper end of thevertical shaft 1 has mounted thereon a horizontal carrier la upon whichis placed a multicomponent glass 2 made in accordance with theinvention. For the purpose of heating this glass a heater or 40radiation means 6 is attached to one end of a lever 7 which is pivotallysupported in a bearing 8a in the wall of the shell so as to be pivotallymovable by the handle 8 arranged outside of the shell to a positionabove the glass 2 as shown in solid lines. Now the multi- 4 componentglass is heated to the desired glowing condition. When this has beendone, the heater 6 is pivoted by the handle 8 away from the radiationrange of the glass 2 and is arrested in a position shown in dash lines.Now the electron gun 5 is operated so that the glass vaporizes and isdeposited on the substrate 9 to be vapordeposited.

What we claim is:

1. An improved method for producing a layer of a multi-component glasson a substrate comprising the steps of:

A. maintaining a multicomponent glass in a melted condition either undera pressure not greater than about 10 torr or in a protective gasatmosphere for a time sufficient to substantially completely degas saidglass, said glass containing not more than about 10 percent by weight ofcombined alkali oxide, said glass consisting essentially of thefollowing composition:

SiO 35 percent by weight,

B 0 5 25 percent by'weight, Li O 0 5 percent by weight, Na O 0.5 10percent by weight,

K 0.5 percent by weight, A1 0 3 40 percent by weight, CaO 0 25 percentby weight, BaO 0 25 percent by weight, TiO 0 percent by weight, and V 00 50 percent by weight, B. pouring the so treated glass into a mold, C.cooling the so treated glass until solid, D. forming a pane of the socooled glass, E. inserting said pane into an electron beam furnace,

F. heating said pane of glass to a glowing condition,

G. bombarding said pane of glass with an electron

2. The process of claim 1 wherein said protective gas atmospherecomprises dry air.
 3. The process of claim 1 wherein, in said electronbeam furnace, said multicomponent glass having a thermal co-efficient ofexpansion not greater than about 40 X 10 7/*C. in the range from about20* to 300*C.